The practice of eliminating unhealthy/biofouling microorganisms in water dates back to ancient civilizations. There are several methods to disinfect water, including brackish water, waste water and cooling water. Electrochemical methods can produce disinfection agents. Disinfection is not sterilization. Disinfection refers to the deactivation of “pathogen” (disease causing) microorganisms, whereas sterilization refers to the deactivation of all microorganisms present. Mechanisms for microorganism deactivation include the modification of, or attack on: the cell wall (e.g., rupture, property modification, etc.); the cell internal components (e.g., protoplasm or nucleic acid modification, alteration of protein synthesis, fatal induction of abnormal redox processes, etc.); and the enzymatic activity.
The most common disinfecting agents have properties as oxidants. This makes the disinfectants useful for the deactivation of most microorganisms, but also brings about undesirable effects, such as the discoloration of dyes, the corrosion of some metals, and the attack on some organic substances. These spurious properties of oxidants in some applications create an extra “load” thereby requiring the production of extra amounts of the disinfecting agent, increasing the corresponding costs, or requiring care to maintain the disinfecting agent concentration below levels that can cause damage, increasing collateral costs associated with treatment. Furthermore, some disinfecting agents produce “disinfection by-products” (DBP) upon their addition or reaction with organic substrates. Such DBP's are frequently toxic, as is the case with most chlorinated hydrocarbons. The main disinfectant agents produced via electrochemistry can be classified according to the oxidizing element: chlorine-based (e.g., chlorine gas, hypochlorite, hypochlorous acid, and chlorine dioxide); oxygen-based (e.g., ozone, hydrogen peroxide, and hydroxyl radicals); and others (e.g., permanganate, ferrate, ions of other transition metal ions (for example, copper and silver), percarbonate, persulfate, other halogens (for example, hypobromite, hypobromous acid) and derivatives (for example, mixed chlorine and bromine oxides), and the electrochemical manipulation of pH (i.e., the production of high levels of acidity or basicity)).
Reliable measurement of disinfection agents, especially chlorine-based or bromine-based hypohalites, has proven difficult in some circumstances. Automated water sampling systems can grab water samples for manual titration. However, this process is time consuming, does not produce near real-time measurements, and may not be performed in inaccessible systems. In some situations, sensors, based on amperometry, can be used. Amperometry is a generic term for a measurement that consumes the analyte and produces a measurable current that can be correlated to an amount of hypohalite or total residual oxidant in the solution. Total residual oxidant (TRO) measurement is often referred to as the measurement of an oxidant species or, more specifically, the measurement of chlorine using an electrochemical sensor or a titration-based approved standard method. Laypersons refer to electrolytic halogenation as chlorine, chlorination, or electrolytic chlorine generation (ECG) without particular attention to actual speciation.
However, finding the proper sensor to use for long-term measurement of TRO, especially in saline aqueous environments, has been difficult. Current chlorine amperometry sensors are not able to make functional long-term measurements without frequent and costly maintenance and calibration. In electrochemistry two or more electrodes may make a sensor that provides a measurement. The TRO sensor is a minimum three-electrode sensor that is also an amperometric sensor. Current amperometric sensors have many drawbacks.